Mine firing control system

ABSTRACT

1. In a device of the class described, the combination of a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminals, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, electroresponsive means connected between said center tap and the negative terminal of said source of energy, and means for selectively discharging said condensers.

United States Patent [191 Mounce et al.

[ MINE FIRING CONTROL SYSTEM Primary Examiner-Robert F. Stahl [75] Inventors: Whitman D. Mounce; Ralph W.

Mann, both of Washington, DC. EXEMPLARY CLAIM 1. In a device of the class described, the combination of a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminals, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, electroresponsive means connected between said cen- 849 e 101 h t 227 3:1 027 a 1.01 n HM em FO e .7 MWC a "0o 8 my S mmm mm m 3 m m 4 mm mm w mm m mm w M. w mm v NW3 0 m mn v TIN A 5 mmM u "8 O m N m .w .0 d S e S S "H p nil A F A UIF 1] 1 2 3 2 I 2 00 7 2 2 555 .l. [.l. [[1

ter tap and the negative terminal of said source of energy, and means for selectively discharging said condensers.

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3,85OJOO PATENTEL NOV 2 619 SHEET 2 OF 2 MINE FIRING CONTROL SYSTEM This invention relates to a firing control system for submarine mines and more particularly to a mine firing control system in which electronic tube networks employing no moving parts are selectively controlled in predetermined time relation in response to signals received through the water by a signal detecting device.

In certain types of mines, it is the practice to cause the mine firing mechanism to respond to a signal induced by the magnetic field associated with a vessel in motion when the vessel is in the vicinity of the mine, such response of the mine being effective to arm the mine or place it in condition to receive a second signal induced by the magnetic field. In the event that the second signal is received within a predetermined period of time after the mine has been armed, the mine is exploded. However, if a second signal is not received during the period in which the mine remains armed, the mine firing control mechanism is restored to normal without firing the mine.

In firing control mechanisms heretofore proposed for controlling the firing of a mine in the manner described hereinabove, it has been the usual practice to employ time measuring devices comprising mechanical elements such as switches controlled by step-by-step motors, rotary motors, clock movements, escapement devices, dashpots and the like. Such time measuring devices have not proved altogether satisfactory in service for the reason that mechanical devices, because of the relatively large mass of the elements and the necessity of employing moving parts therein, are particularly susceptible to damage or injury thereto as the result of the shock or blow which the time measuring device receives at the moment the mine in which it is mounted strikes the water or the bed of the sea at the time of planting of the mine. Such shocks are particularly intense in the case where the mine is launched from an aircraft in flight and various expedients, such as attaching a parachute to the mine or dropping of the mine from a low altitude, have been resorted to in order to reduce the shock to a value which will not damage the mine firing control mechanism.

Furthermore, in the devices of the prior art, various types of magnetic relays have been employed for the purpose of controlling those elements of the mechanism which draw an appreciable current. It has been found that such relays produce stray magnetic fields which interfere with the proper functioning of the mechanism in response to the earths magnetic field and often are the cause of misfires or variations in sensitivity of the mine.

Another disadvantage of the mechanisms of the prior art is their susceptibility to being fired by sweeping apparatus which produces rapidly varying magnetic fields thereby to induce signals in the mine firing mechanism which cause the mechanism to respond and destroy the mine. It is the practice to place such sweeping apparatus on an aircraft whereby a large area of the surface of the sea may be rapidly swept thereby reducing the amount of equipment necessary for this purpose.

In the arrangement of the present invention, certain of these difficulties are avoided by the employment in the firing control system for a mine of electrical elements having no moving parts, such elements comprising electronic tubes, transformers, condensers and re sistors which are rugged and are comprised of static elements thereby substantially eliminating the possibility that these elements will be damaged by the shocks associated with the launching of the mine and the mine be rendered inoperative by reason of such damage. Because of the absence of moving parts, the mine firing mechanism of the present invention may be easily potted, the latter being a process wherein the complete mine firing mechanism is dipped in wax or the like for the purpose of producing a rigid. structure when the wax hardens thereby to reduce the likelihood of darnage due to shock. It is obvious that mechanisms employing moving parts are not susceptible to potting as such treatment would prevent operation of the movable elements and would render the mechanism inoperative.

The absence of electro-mechanical relays in the arrangement of the present invention eliminates the production of stray fields thereby reducing the possibility of misfires and variations in the sensitivity of the system. The system is also provided with means whereby after a first signal is induced by a change in the magnetic field in the vicinity of the mine, the system is rendered unresponsive to a second signal for an appreciable period of time thereby to eliminate the possibility of sweeping the mine by the employment of aircraft as an aircraft carried sweep will pass from the vicinity of the mine, after initiating a first signal, during the period when the firing control system of the mine is unresponsive to a second signal thereby failing to produce destruction of the mine by said second signal.

More specifically, the mine firing control apparatus of the present invention comprises a coil in which are induced electrical currents of opposite polarities when the magnetic field adjacent the mine is disturbed by the passage of a vessel in the vicinity thereof, such disturbance of the field being hereinafter referred to as the magnetic signature of the vessel. his well known that the magnetic signature varies under different portions of a vessel and that the currents induced in the coil change in magnitude and polarity in accordance with the magnetic signature. The coil is connected to a balanced network comprising a magnetic amplifier having a pair of secondary windings connected in series opposing in the network and a pair of primary windings connected in series and supplied with intermittent pulses of energy from a cold cathode tube relaxation oscillator, the pulses of current being sufficient to saturate the cores of the magnetic amplifier. The network is provided with an output transformer connected to a pair of cold cathode tubes, the arrangement being such that when a current of one polarity is induced in the coil by passage of a vessel in the vicinity of the mine, the magnetic amplifier is unbalanced in one direction to cause the output transformer to discharge one of the cold cathode tubes whereas if a current of the opposite polarity is induced in the coil, the other of the cold cathode tubes is discharged.

Each of the cold cathode tubes is connected to the grid of one of another pair of cold cathode tubes, each of which operates when energized to discharge a pair of condensers connected to the respective ends of a potentiometer. The ends of the potentiometer are normally at ground potential and a center tap on the potentiometer is connected to the grid of a detonator firing cold cathode tube thereby to normally maintain said tube in unenergized condition. When one of said condensers is discharged by reason of a signal of -.one polarity being induced in the coil, the voltage of one end of the potentiometer is raised but not sufficiently to raise the voltage of the center tap thereof to a value which will cause the detonator firing tube to ignite. The condenser proceeds to recharge and if the other condenser is not discharged by a signal of the reverse polarity being induced in the coil, the system will return to normal. However, if during a period of approximately two minutes after the first condenser begins to charge, the other condenser is discharged, the voltage of the other end of the potentiometer is raised to a value such that the voltage of the center tap of the potentiometer exceeds the igniting voltage of the detonator firing tube thereby to cause ignition thereof and firing of the mine detonator.

In order to prevent sweeping of the mine by aircraft carried sweeps, an arrangement is provided in the systern whereby the relaxation oscillator which supplies pulses of energy to the balanced network is prevented .from operating for a period of approximately three seconds after a current is induced in the coil by a change in the magnetic field in the vicinity of the mine thereby preventing a current of reverse polarity from affecting the system until an interval of time of sufficient duration has elapsed to make certain that the aircraft has left the vicinity. This is accomplished by a cold cathode tube connected to the potentiometer and arranged to be fired whenever one of the condensers is discharged.

Firing of the latter tube reduces the voltage across the relaxation oscillator to a value which renders it inoperative and simultaneously initiates the charging of a condenser which, after three seconds, charges sufficiently to cause operation of an electronic tube network arranged t deenergize the last mentioned cold cathode tube thereby to permit the relaxation oscillator to again function in a normal manner. An anticountermine switch which closes upon receipt of severe shocks produced either deliberately by explosives placed in the water by the enemy or by the explosion of other mines or torpedoes in the vicinity of the mine operates to fire the last mentioned cold cathode tube which functions in the manner previously described to render the relaxation oscillator temporarily inoperative.

By the use of cold cathode tubes which require no filament current for heating their cathodes and by employing an intermittently operating relaxation oscillator, the drain on the batteries in the mine is kept so low as to compare favorably with other types of mine firing mechanisms in length of life after the mine has been planted in enemy waters. The magnetic amplifier and the cold cathode tubes also render the system as sensitive to the changes in a magnetic field as any other of the mechanisms of the prior art while eliminating the necessity of employing elements having moving parts.

One of the objects of the present invention is the provision of a new and improved mine firing control system in which the foregoing disadvantages are obviated and which possesses all of the advantages of arrangements heretofore proposed for this purpose.

Another object of the invention is to provide a mine firing control system in which electrical elements and networks having no moving parts are employed thereby rendering the system susceptible to potting.

An additional object of the invention resides in -a novel and improved arrangement in which a magnetic amplifier and electronic tubes are employed in a mine firing control circuit without producing undue drain on the batteries employed therein.

A further object of the present invention is to provide a mine firing control system in which means are provided for rendering the system unresponsive to the second one of a pair of signals when said signals are not spaced by more than a predetermined minimum period of time thereby to eliminate any possibility of the mine being swept by aircraft carried sweeps.

Still another object of the invention is the provision of a mine firing control system in which no electromechanical relays or other devices which produce strong magnetic fields are employed thereby to reduce v the likelihood of the mine failing to fire or firing prematurely by reason of changes in the sensitivity of the firing control system caused by such stray fields.

Another object of the invention is to provide a simple anti-countermine arrangement requiring very little additional equipment and which will prevent explosions in the vicinity of the mine from firing the mine thereby rendering it immune to explosions deliberately caused by the enemy or to other sudden shocks.

Still other objects, advantages and improvements will become apparent from the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a sectional view with certain parts in elevation of a mine suitable for use with the mine firing control circuit of the present invention; and

FIG. 2 illustrates in diagrammatic form a complete circuit suitable for use with the mine of FIG. 1 according to a preferred embodiment of the invention.

Referring now to the drawings in which like numerals of reference are employed to designate like parts throughout the several views, there is shown in FIG. 1 a mine indicated generally by the numeral 10 having a casing 11 adapted to be sealed by a cap or cover 12 secured thereto as by the bolts 13, a gasket 14 being preferably arranged between the cover and the casing to insure a watertight joint therebetween. There is arranged within the casing 11, a wall or partition 15 welded or otherwise secured to the casing 11 and provided with a well 16 for a purpose to be hereinafter disclosed.

Secured on the exterior of the well 16 is an annular support 17 adapted to receive one end of an. induction pickup coil 18 comprising a relatively large number of turns of wire 19 arranged about a rod 21 of iron or composed of a material sold under the trade name of Permalloy, the rod and wire being enclosed in a supporting and protective sheath 22. The other end of the coil is disposed within a recessed portion 23 of the casing 11, suitable pads or cushions 24 being arranged between the ends of the coil and the recessed portion 23 and support 17 respectively to prevent damage or injury to the coil as the mine is launched.

The partition 15 also forms a chamber 25 within which is arranged an explosive charge 26 of TNT or the like sufficient to destroy or damage a vessel and to impart a negative degree of buoyancy to the mine whereby the mine is adapted to come to rest on the bed of a body of water after being launched therein. A suitable watertight filler opening 20 is provided by means of which the charge 26 is introduced within the mine casing.

There is also provided within the chamber 25 a well i 27 within which is arranged an explosive booster charge 28 as is well known in the art to which the invention pertains. There is also arranged within the well 27 a hydrostat mechanism comprising a plunger or rod 29 slideably arranged within the support 31 and normally urged outwardly therefrom by a spring 32 is engagement with the collar 33 secured to the plunger. A flexible diaphragm 34 is clamped to the collar 33 as by the nut 35, the diaphragm being maintained in watertight relation with respect to the well 27 as by the bolts 36 and a clamping ring 37. A soluble washer 38 secured to the plunger as by the nut 39 prevents the inward movement of the plunger until the mine has been planted for a period of time sufficient to dissolve or soften the soluble washer. When this occurs, the detonating device 41 is moved by the plunger into operative relation with respect to the booster charge 28. The detonating device 41 is connected electrically by means of a pair of conductors which pass through a duct 42 to the various other components of the mine mechanism.

The mine is also provided with a recess or well 43 within which is arranged a hydrostat 44 adapted to set an arming clock 45 into operation in response to the movement of the hydrostat under the influence of the surrounding water. The arming clock may be of any type suitable for the purpose adapted to close circuits between a plurality of pairs of conductors within the duct 46 and connected to the other components of the mine mechanism as will hereinafter be described. A suitable arming clock is described and claimed in the copending application of James B. Glennon et al., for Firing Mechanism For A Submarine Mine, application Ser. No. 395,230, filed May 26, 1941.

The mine firing mechanism comprises a signal amplifying device indicated generally by the numeral 47 arranged preferably within a suitable resilient cushion or pad 48 fitted within the mine case in abutting relation with the partition and the cap 12, a battery 49 within the well 16 being provided for supplying the electrical energy required for the operation of the mine firing control mechanism. The battery 49 is preferably disposed within a suitable pad 51 of yieldable material, the pads 48 and 51 which are composed of rubber or the like being for the purpose of preventing injury to the amplifying device or the battery respectively when the mine is launched. A plurality of fins 52 secured to the mine casing 11 in any suitable manner are employed to direct and steer the mine during the launching thereof within a body of water. The pad 48 is provided with an aperture 53 therein within which is arranged the electrical cable 54 for establishing external electrical connections from the device 47 to the other components of the mine.

Referring now to FIG. 2 of the drawings, the circuit connections extending between the various elements of the mine firing system are diagrammatically illustrated therein. The induction pickup coil 18, hereinafter referred to as a search coil, is electrically connected by the conductor 55 to ground, the other end of the coil being connected by the conductor 56 to a magnetic amplifier network indicated generally by the numeral 57. The magnetic amplifier is intermittently energized by a cold cathode tube relaxation oscillator, designated generally by the numeral 58, having a condenser 61 connected across the plate circuit thereof in series with the primary winding of an isolation transformer 62, the condenser being charged from the battery 49 through the resistors 63 and 64 when the armingclock switch 65 is closed. The grid of the tube 59 is connected to the potentiometer 60, the voltage of which varies with the voltage across the condenser 61.

The secondary winding of the isolation transformer 62 is connected in series with the primary windings 66 of the magnetic amplifier 67 and the filter 68. The magnetic amplifier is provided with cores made of Permalloy or the like which are saturated each time current flows through the primary windings 66, and with secondary windings 69 connected in series opposition as illustrated by the arrows. A variable potentiometer 71 is connected across the windings 69 for the purpose of balancing the outputs thereof when the search coil is not being subjected to changes in the magnetic field adjacent thereto, the magnetic amplifier network 57, which is grounded at 70, also including the primary winding 72 of an output transformer 73 and a resistor 74 connected in series across the secondary windings 69 of the magnetic amplifier 67. i

The secondary winding 75 of the output transformer 73 has one of its ends connected through conductor 76, blocking condenser 77 and conductor 78 to the grid of a cold cathode tube 79, the grid being positively biassed to slightly below the grid firing voltage by the resistor 81 and conductors 82 and 83 connected to the battery 49 as at terminal 84. The other end of the secondary winding 75 is connected through conductor 85, blocking condenser 86, and conductor 87 to the grid of a cold cathode tube 88 which is positively biassed to just below the grid firing voltage by resistor 89 and conductor 91 connected by conductor 83 to the terminal 84 of the battery 49. The secondary winding 75 is provided with an mid-tap 92 connected by conductor 93 and resistor 94 to the grounded conductor 95, the cathodes of the tubes 79 and 88 being connected to conductor 95 by the resistors 96 and 97 respectively to complete the grid circuits thereof. The tubes 79 and 88 have their plate circuits energized from a condenser 98 as will be hereinafter more fully described, the condenser 98 being charged through a circuit extending from the terminal 101 of the battery 49, conductor 102, resistor 99, condenser 98, resistor 94, and grounded conductor 95, the circuit being completed through the grounded negative side of the battery 49.

The cathode of the tube 79 is connected by conductor 103, blocking condenser 104, and conductor 105 to the grid of a cold cathode tube 106, a positive grid biassing voltage being connected to the grid of the tube through the resistor 107 connected to the positively energized conductor 83 thereby to maintain the grid slightly below its firing potential. lln a similar manner, the cathode of the tube 88 is connected by conductor 108, blocking condenser 109 and conductor 1 11 to the grid of a cold cathode tube 112, this gn'd being positively biassed slightly below its firing potential by the resistor 113 connected between the grid and the positively energized conductor 83.

The plate circuit of tube 106 is energized by a condenser 114 which is charged from the positively energized conductor 102, the circuit to ground being completed through conductors 115 and 116, resistor 117, and conductor 118 to the grounded conductor 95. In a similar manner, the condenser 1 l9 energizes the plate circuit of the tube 112, the condenser being charged from the conductor 102, through conductor 121, resistor 122, and conductor 123 connected to the grounded conductor 95. A condenser 120 is connected across the battery conductor 102 and the grounded conductor 95 to maintain the battery voltage constant when high currents are drawn therefrom by the charging of the condensers 98, 114 and 119.

Connected to one side of the condenser 114 at the point 124 is one end of a potentiometer comprised of two resistors 125 and 126, the other end of the potentiometer being connected at the point 127 to one side of the condenser 119. The midpoint 128 of the potentiometer is connected by the conductor 129 to the grid of a cold cathode tube 131, this grid being normally held at ground potential by means of a conductor 132, a condenser 133 and a conductor 134 connected to the grounded conductor 95. The plate circuit of the tube 131 is energized by a condenser 135 which is connected on one side to the grounded conductor 95 and on the other side to the terminal 136 of the battery 49 by conductors 137 and 138 and resistor 139 whereby the condenser 135 is normally maintained charged. The detonating device 41 is connected across the output resistor 141 of the cold cathode tube 131 by a circuit extending from one side of the resistor 141 to conductor 142, the switch 143 of the arming clock 45 when closed, conductor 144, the detonating device 41, and the grounded conductor 95 to the other side of resistor 141.

Connected between the points 124 and 127 of the potentiometer is a pair of similar condensers 145 and 146, the point 147 between the condensers being connected by the conductor 148 and the resistors 149 and 151 to the grid of a cold cathode tube 152. The grid of the cold cathode tube 152 is normally connected to the cathode of the tube by a resistor 153 and conductors 154 and 155 thereby to maintain the grid normally below the firing potential of the tube. A normally open anti-countermine switch 156 is connected between the grid and the anode of the cold cathode tube 152, closure of this switch raising the potential on the grid of the tube above the firing value by shunting the resistor 157 which with the resistor 153 determines the voltage normally applied to the grid of the tube 152. The anode of the tube 152 is connected by the conductors 158 and 159 to the terminal 161 of the battery 49, the cathode of the tube being connected by the conductors 155, 154 and 162 to the cathode resistor 63 which is connected to the negative side of the battery 49.

The anti-countermine switch 156 is preferably of the inertia type of any well-known construction suitable for the purpose and is arranged to prevent firing of the mine when a sudden shock is received such as is caused by the explosion of a torpedo or another mine within the vicinity of the mine 10 or as the result of a countermining operation by the enemy. A suitable inertia switch is disclosed and claimed in the copending application of Seth W. Booth for Inertia Switch And Means Controllled Thereby, application Ser. No. 484,854, filed Apr. 28, 1943.

The system is provided with a cold cathode tube 163 for a purpose to bev more fully disclosed hereinafter, tube 163 having its anode connected through a resistor 164, shunted by a condenser 165, and the conductor 137 to the terminal 136 of the battery 49, the cathode of the tube 163 being connected by the resistor 166 and the conductor 167 to the negative side of the battery 49. The grid of the tube 163 is connected through a resistor 168 and conductors 154 and 155 to the cathode of the tube 152, a condenser 169 being connected between the conductor 154 and the resistor 166 for a purpose to be hereinafter disclosed. The grid of the tube 163 is also connected to the negative side of the battery by the conductor 171 and a condenser 172.

' The arming clock 45 is provided with two sets of contacts and 143 operated by a spring and escapement controlled cam 173, the cam being so arranged that contacts 65 close in one hour after the clock has been started to complete the energizing circuit from the battery 49 to the relaxation oscillator 58, and contacts 143 close in 2 hours to prepare an energizing circuit to the detonating device 41 as will be more particularly disclosed hereinafter, the clock being generally similar to the arming clock disclosed in the aforesaid application of James B. Glennon et al.

The operation of the mine will now be described.

When the mine 10 is planted on the bed of a body of water, the hydrostat 44 in response to hydrostatic pressure starts the arming clock 45. The soluble washer 38 begins to dissolve and after a predetermined period of time it softens sufficiently to permit the hydrostatic pressure to act upon the diaphragm 34 which inserts the detonating device 41 into the booster charge 28. After an hour has elapsed, the cam 173 which rotates in the direction of the arrow turns sufficiently to cause the contacts 65 to close and closure thereof completes a charging circuit to the condenser 61 from the positive side of the battery 49 through the conductor 174, the contacts of the switch 65, the conductor 175, the primary winding of the transformer 62, the condenser 61, and the resistors 64 and 63 to the negative side of the battery. As the condenser charges, the voltage across 1 the potentiometer 60, to which the grid of the tube 59 is connected, and the plate circuit of the tube gradually increases to a value in excess of the critical voltage thereof and causes the tube 59 to break down and discharge the condenser 61 which immediately thereafter begins to recharge to repeat the cycle.

The primary winding of the transformer 62 is energized for a brief period by the discharge of the condenser 61 through the tube 59 and induces a voltage in its secondary winding which is applied to the primary windings 66 of the magnetic amplifier 67 through the filter network 68. The pulse of current through the primary windings 66 is sufficient to cause saturation of the cores of the magnetic amplifier and, as the secondary windings 69 of the magnetic amplifier are connected in opposition as indicated by the arrows, no unbalance voltage appears across the primary winding 72 of the transformer 73 if no signal is being received from the search coil 18 and the potentiometer 71 has been previously adjusted to balance the outputs of the secondary windings 69. The relaxation oscillator 58 is designed to generate from two to four pulses per second and, when no signal is produced by the search coil 18, the pulses.

generated by the relaxation oscillator continue to saturate the cores of the magnetic amplifier 67 at a uniform rate without, however, producing any voltage across the primary winding 72 of the transformer 73.

Let it now be assumed, by way of example, that sufficient time has elapsed for the arming clock 45 to close contacts 143 and that a vessel having a magnetic signature which varies under each portion of the vessel moves within the vicinity of the mine or passes above the mine. As the first portion of the magnetic signature moves into proximate relation with respect to the search coil 18, an electromotive force is generated within the search coil of one polarity or the other and this electromotive force produces a current which passes through the opposed secondary windings 69 causing one of the cores to become more saturated and the other of the cores to become less saturated each time the relaxation oscillator pulses thereby upsetting the balance of the magnetic amplifier network 57 and producing a potential across the primary winding 72 of the transformer 73. This off balance voltage has an amplitude which is proportional to the current flowing through the secondary windings 69, the amplitude as the pulse rises being greater and of shorter duration than when the pulse decays. When the voltage induced in the search coil 18 by the passage of a vessel in the vicinity thereof reverses by reason of a change in the magnetic signature of the vessel, the direction of the unbalanced voltage across the primary winding 72 of the transformer 73 is also reversed.

For the purpose of description, it is assumed that the direction of the potential appearing across the primary winding 72 is such that the right hand end of the secondary winding 75 become positive and the left hand end becomes negative when a vessel initially passes adjacent the search coil 18. When this occurs, the grid of the cold cathode tube 88 is made more negative and the grid of the cold cathode tube 79 is raised above its firing potential by a circuit extending from the right hand end of secondary winding 75, conductor 76, condenser 77 and conductor 78, the cathode of the tube 79 being connected through resistor 96, conductor 95, re sistor 94, and conductor 93 to the mid-tap 92 of the secondary winding 75. The tube 79 discharges the previously charged condenser 98 through the resistors 94 and 96, the discharge of the condenser 98 lowering the voltage between the plate and cathode of the tube 88 and the drop across the resistor 94 causing a negative impulse to appear on the grid of the tube 88, both of these effects preventing firing of the tube 88 when the voltage across the primary winding 72 of the transformer 73 reverses momentarily upon decay of the voltage induced in the search coil 18.

The voltage appearing across the resistor 96 when the condenser 98 discharges is applied through conductor 103, the condenser 104, and conductor 105 to the grid of the cold cathode tube 1116 thereby raising the potential of the grid above the firing value and causing this tube to discharge the previously charged condenser 1 14 connected thereacross. Discharge of the condenser 114 raises the potential of the point 124 to within approximately volts of the battery potential and, since the point 127 is still maintained at ground potential by reason of its connection to the grounded conductor 95 through conductor 121, resistor 122, and conductor 123, the potential of the point 128 connected to the grid of the tube 131 is raised to substantially one half the voltage of the point 124 which potential is just below the firing potential of the tube 131 which remains inactive for the time being.

The condenser 114 immediately begins to recharge and if a current of reverse polarity to that initially induced in the search coil 18 is not induced in the search coil within two minutes, the system returns to normal as the constants of the charging circuit connected to the condenser 114 are of such value as to require a period of two minutes to elapse before the condenser is fully recharged. If during this two minute period, a current of the same polarity is received from the search coil, the tubes 79 and 106 operate either to discharge the potential now appearing across the condenser 114 thereby reinitiating the two minute period or, if the potential is too low to be discharged, to permit the condenser 114 to continue to recharge to complete the initial two minute period.

However, if during this two minute period the magnetic signature of the vessel induces a voltage of reverse polarity in the search coil 18, the left hand end of the secondary winding 75 of the transformer 73 becomes positive when the relaxation oscillator pulses thereby to raise the potential of the grid of the tube 88 above the firing value thereof, the right hand end of the secondary winding 75 becoming negative thereby to prevent firing of the tube 79. The tube 88 discharges the condenser 98 which has been rapidly recharged after having been discharged by the tube 79 as previously described. Discharge of the condenser 98 by the tube 88 reduces the voltage across the plate and cathode of the tube 79 and the voltage drop across the resistor 94 causes a negative impulse to appear upon the grid of the tube 79 thereby to further insure that this tube will not be fired by the momentary reversal of polarity which occurs in the secondary winding of the transformer 73. Discharge of the condenser 98 by the tube 88 also causes a voltage drop across the resistor 97 which applys a voltage through the conductor 108 connected to one end thereof, the condenser 109, and conductor 111 to the grid of the tube 112 thereby causing this tube to fire and discharge the previously charged condenser 119 connected thereacross.

When the condenser 119 discharges, the potential of the point 127 is raised to within about 10 volts of the battery potential and, since the condenser 114 has not become fully charged within the period of less than two minutes which has elapsed since the condenser 1 14 was discharged, the voltage of the point 124 is still above ground potential so that the voltage of the point 128 is greater than one half the voltage of the point 127 and is therefore above the firing voltage of the grid of the tube 131. Tube 131, therefore, discharges the previously charged condenser 135 through the resistor 141 thereby to fire the detonating device 41 which is connected across the resistor 141 by a circuit extending from one end of the resistor 141 through the conductor 142, switch contacts 143 of the arming clock 45, the conductor 144, detonating device 41 and the grounded conductor to the other side of the resistor 141. When the detonating device 41 is fired, it explodes the mine thereby to damage or sink the vessel which has passed a sufficient distance over the mine in the period between the discharge of the condenser 114 and the discharge of the condenser 119 to present a particularly vulnerable portion of the vessel to the effects of the explosion.

It is sometimes desirable to replace the detonating device 41 by a ship-counter of any suitable type which may be set up to count a predetermined number of vessels before destroying the next succeeding vessel. In the event that such a ship-counter is employed in the system, each discharge of the condenser is arranged to count one vessel, the condenser 135 requiring approximately three minutes in which to become recharged through the resistor 139 thereby to permit a dead period following each actuation of the shipcounter. This arrangement prevents the enemy from sweeping the mine by passing a rapidly reversing magnetic field over the mine or in its vicinity as changes in the magnetic field during the dead period will have no effect on the ship-counter.

It will become apparent from the foregoing description and a study of the circuits that if the magnetic signature of the vessel produces firing of the tube 88 and subsequent firing of the tube 79 within a period of less than two minutes, the foregoing sequence of events will be repeated in reverse order and the condenser 135 will be discharged to fire the detonating device 41 or count a ship, as the case may be.

The tubes 152 and 163 and their associated circuits are arranged to provide a dead period in the operation of the entire system by maintaining the relaxation oscillator 58 inoperative for a predetermined period of time. This is done for a twofold purpose. Firstly, a dead period of approximately three seconds is provided after a discharge of either of the condensers 114 or 1 19 before the other of said condensers can be discharged thereby to reduce the possibility of the mine being swept by a sweep carried by an aircraft as the latter travels too rapidly to be in the vicinity of the mine three seconds after the initial generation of a current of one polarity in the search coil 18 by the sweep, which would be necessary if the sweep is to produce a current of reverse polarity in the search coil after a period of three seconds has elapsed. Secondly, a similar three second dead period is provided by closure of the anticountermine switch 156 when the enemy deliberately causes an explosion in the vicinity of the mine or a mine in the same mine field is exploded by the passage of a vessel adjacent thereto.

The manner in which the tubes 152 and 163 operate will now be described. When either of the condensers 114 or 119 is discharged, the potential of the point 147 connected by the condenser 145 to the point 124 and by the condenser 146 to the point 127, is raised above the firing potential of the grid of the tube 152 to which it is connected by the conductor 148, the resistor 149, and the resistor 151, thereby causing the plate circuit of the tube 152, which is connected to the battery 49 by a circuit extending from the terminal 161 of the battery 49, through the conductors 159 and 158, the tube 152, the conductors 155, 154 and 162, and the cathode resistor 63 to the negative side of the battery, to break down and produce a voltage drop in the cathode resistor 63. This drop reduces the voltage across the condenser 61 of the relaxation oscillator 58 and the condenser 61 is unable to charge to a voltage high enough to fire the tube 59 thereby preventing pulsing of the relaxation oscillator and rendering the magnetic amplifier network 57 inoperative to respond to any signals generated in the search coil 18.

This condition continues for a period of approximately three seconds during which the condenser 172 is being charged by the voltage drop across the resistor 63 through a circuit extending from one side of the resistor 63 through the conductors 162 and 154, the resistor 168, the condenser 172, and the conductor 171 to the other side of the resistor 6.3. When the condenser 172 becomes charged, it raises the potential on the grid of the tube 163 above the firing potential of this tube and the tube 163 fires through a circuit extending from the terminal 136 of the battery 49 through the conductor 137, the resistor 164 shunted by the condenser 165, the plate-cathode path of the tube 163, resistor 166 and conductor 167 to the negative side of the battery. Firing of the tube 163 causes transmission of a positive impulse through the condenser 169 and the conductors 154 and to the cathode of the tube 152 thereby deenergizing this tube by reducing the voltage across its plate circuit, the tube 163 becoming deenergized when the condenser is charged sufficiently by the voltage drop across the resistor 164 to cause the voltage across the plate circuit of the tube 163 to be reduced below a value which will sustain an arc within the tube. Deenergization of the tube 152 permitsthe relaxation oscillator to resume its normal pulsing thereby allowing the magnetic amplifier network 57 to again respond to currents induced in the search coil 18.

Closure of the anti-countermine switch 156 by reason of a shock sustained by the mine shunts the resistor 157 thereby to increase the potential on the grid of the tube 152 to a value which causes this tube to tire thus repeating the sequence of events described hereinabove to render the relaxation oscillator 58 inoperative for a period of three seconds. This prevents such shocks from destroying the mine by causing movement thereof which movement will normally induce a current in the search coil 18 and produce a false operation of the system. Production of a three second dead period by operation of the anti-countermine switch 156 will not affect the charges on either of the condensers 114 or 119 so that reception of two signals of opposite polarity from the search coil 18 within a period of two minutes will cause detonation of the mine or counting of a ship, as the case may be, and upon the elapse of any three second dead period, the relaxation oscillator 58 will commence to pulse at a normal rate and the system will function in the same manner as heretofore.

Briefly stated in summary, the present invention contemplates the provision of a new and improved mine firing control system adapted to fire a mine when it receives two successive actuations from the magnetic signature of a vessel in the vicinity of the mine, which actuations produce signals of opposite polarity within a search coil within a predetermined period of time, the mine firing system being constructed to have no moving parts so that the mine firing system will not be susceptible to damage or injury by reasonof the shocks caused by launching thereof. The invention also contemplates the use of elements which will produce very little drain on the mine battery and will, therefore, assure long life thereof and it is further contemplated that the system will be difficult to sweep by ordinary methods and will be protected against counter-mine shocks however produced by means which is simple, rugged, and extremely rapid in operation. The system of the invention has been arranged to eliminate the use of all magnetic relays thereby preventing the production of spurious magnetic fields which may afiect the operation of the system by causing the generation of false signals by the search coil employed in the system or causing improper operation of the magnetic amplifier.

Although, in accordance with the provisions of the patent statutes, this invention has been described in concrete form with reference to a preferred embodiment thereof which gives satisfactory results, it will be understood that this form is merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or the scope of the annexed claims.

The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a device of the class described, the combination of a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, electroresponsive means connected between said center tap and the negative terminal of said source of energy, and means for selectively discharging said condensers.

2. In a device of the class described, the combination of a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiom eter connected between said other plates of said condensers, a center tap on said potentiometer, electroresponsive means connected between said center tap and the negative terminal of said source of energy, a pair of electronic tubes each having a plate circuit and a grid, means for connecting the plate circuits of said tubes across said condensers respectively, and means for selectively energizing each of said grids.

3. In a device of the class described, the combination of a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, a pair of electronic tubes each having a plate circuit and a grid, means for connecting the plate circuits of said tubes across said condensers respectively, means for selectively energizing each of said grids whereby the electronic tubes will discharge the respective condensers, an electronic device having an input circuit and an output circuit, an electroresponsive device connected to said output circuit and controlled thereby, and means connecting said input circuit to said center tap and to the negative terminal of said source for firing said electronic device when both of said condensers are discharged within a predetermined period of time.

4. In a device of the class described, the combination of means for producing signals of opposite polarities, a

pair of energy storage devices, means for gradually storing energy therein, means controlled by said signals for selectively discharging energy from said energy storage devices in accordance with the polarities of said signals, a circuit, means for closing said circuit responsive to discharge by said discharging means of energy from one of said devices when less than a predetermined amount of energy has been stored in the other of said devices by said storing means, and electroresponsive means in said circuit operated upon closure thereof.

5. In a device of the class described, in combination: a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, a pair of electronic tubes each having a plate circuit and a grid, means for connecting the plate circuits of said tubes across said condensers respectively, means for selectively energizing each of said grids whereby the electronic tubes will discharge the respective condensers, an electronic device having an input circuit and an output circuit, an electroresponsive device connected to said output circuit and controlled thereby, means connecting said input circuit to said center tap and to the negative terminal of said source for firing said electronic device when both of said condensers are dis charged within a predetermined period of time, a third condenser connected across said output circuit, and means to charge said third condenser within a predetermined interval.

6. In a device of the character disclosed, the combination of a mine comprising means responsive to the magnetic field adjacent a moving paramagnetic object for producing signals of opposite polarities in accordance with changes in said magnetic field, a pair of energy storage devices, means for gradually storing energy therein, means controlled by said signals for selectively discharging the energy stored in said energy storage devices in accordance with the polarities of said signals, a circuit, means responsive to the amount of energy stored in said devices for controlling said circuit, and means in said circuit for firing the mine when the amount of energy stored in each of said devices is less than a predetermined maximum.

7. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with changes in the magnetic field, a pair of condensers, means for gradually charging said condensers, means controlled by said signals for selectively discharging said condensers in accordance with the polarities of said signals, a circuit, means responsive to the charges on said condensers for controlling said circuits, and means in said circuit for firing the mine when the charge on each of said condensers is reduced to less than a predetermined value.

8. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with changes in the magnetic field, a pair of condensers, means for gradually charging said condensers, a pair of electronic tubes, means controlled by said signals and including said tubes for selectively discharging said condensers in accordance with the polarities of said signals, a circuit, means responsive to the charges on said condensers for controlling said circuit, and means in said circuit for firing the mine when the charge on each of said condensers is reduced to less than a predetermined value.

9. In a submarine mine for damaging the vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with changes in the magnetic field, a pair of condensers, means for slowly charging said condensers, a pair of electronic tubes, means controlled by said signals and including said tubes for selectively discharging said condensers in accordance with the polarities of said signals, a circuit, means responsive to the charges on said condensers for controlling said circuit, and means in said circuit for firing the mine when both of said condensers are discharged within a predetermined period of time.

10. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a source of electrical energy having positive and negative terminals, a pair of resistors, a pair of condensers each having one plate connected to said positive terminals and the other plate connected in series with one of said resistors to said negative terminal, a potentiometer connected between said other plates of the condensers, a center tap on the potentiometer, a pair of electronic tubes each having a plate circuit and a grid, means for connecting the plate circuits of said tubes across said condensers respectively, means controlled by said signals for selectively energizing said grids in accordance with the polarities of said signals thereby to discharge the respective condensers, an electronic device having an input circuit and an output circuit, mine firing means connected to said output circuit and controlled thereby, and means connecting said input circuit to said center tap and to the negative terminal of said source for firing the electronic device when said condensers are both discharged within a predetermined period of time.

11. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with changes in the magnetic field, a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series withone of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, means controlled by said signals for selectively discharging said condensers in accordance with the polarities of said signals, an electronic device having an input circuit and an output circuit, a mine firing device connected tosaid output circuit and controlled thereby, means connecting said input circuit to said center tap and to the negative terminal of said source for firing said electronic device when both of said condensers are discharged within a predetermined period of time, a third condenser connected to energize said output circuit, and means for charging said third condenser within a predetermined interval.

12. In a system of the class described, the combination of means for producing signals of opposite polarities, means including a relaxation oscillator cooperating with said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, an electroresponsive device, means responsive to the production of voltages of opposite phase within a predetermined period of time for energizing said electroresponsive device, and means responsive to shocks applied to the system for rendering said relaxation oscillator inoperative for a predetermined interval.

13. In a system of the class described, the combination of means for producing signals of opposite polarities, means including a relaxation oscillator cooperating with said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, means responsive to production of a voltage of one phase for rendering said relaxation oscillator inoperative for a predetermined interval, an electroresponsive device, and means cooperating with said last named means and responsive to theproduction of a voltage of opposite phase within a predetermined period of time after said predetermined interval has elapsed for energizing said electroresponsive device.

14. In a system of the class described, the combination of means for producing signals of opposite polarities, means including a relaxation oscillator cooperating with said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, means responsive to production of a voltage of one phase for rendering said relaxation oscillator inoperative for a predetermined interval, an electroresponsive device, means cooperating with said last named means and responsive to the production of a voltage of opposite phase within a predetermined period of time after said predetermined interval has elapsed for energizing said electroresponsive device, and means responsive to shocks applied to the system for operating said means for rendering said relaxation oscillator inoperative for a predetermined interval.

15. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, means responsive to production of a voltage of one phase for rendering said relaxation oscillator inoperative for a predetermined interval, and means cooperating with said last named means and responsive to production of a voltage of opposite phase within a predetermined period of time after said predetermined interval has elapsed for firing the mine.

vice conducting when said second and third devices are rendered conducting successively within said interval of time.

22. In a device of the character disclosed, the combination of an output circuit including a first gaseous discharge device having a control grid, means for rendering said first discharge device conducting to close said circuit when the voltage on the control grid is increased by a predetermined amount above a predetermined value, a pair of gaseous discharge devices, means for rendering said pair of discharge devices conducting selectively, means adapted to be rendered effective as either one of said pair of discharge devices is rendered conducting to apply a first voltage to said control grid which maintains a potential thereon in excess of said predetermined value for a predetermined interval of time, and means adapted to be rendered effective as the other of said pair of discharge devices is rendered conducting during said interval of time to apply a second voltage to the control grid which is additive with respect to said first voltage thereon and increases the potential on the grid by said predetermined amount whereby the first discharge device is rendered conductmg.

23. In a device of the class described, the combination of a pair of energy storage devices, means for gradually storing energy therein, means for selectively and substantially instantaneously discharging energy from said storage devices, a circuit, means responsive to discharging of one of said storage devices for applying an energy pulse to said circuit, means responsive to discharging of the other of said storage devices within a predetermined time after discharging of the first of said devices for applying an energy pulse to said circuit which is additive with respect to said first-named pulse applied thereto, means for closing said circuit when the additive energy pulses applied thereto exceeds a predetermined value, and electroresponsive means in said circuit adapted to be operated as the circuit is closed.

24. In a device of the class described, the combination of a pair of energy storage devices, means for gradually storing energy therein, means for selectively and substantially instantaneously discharging energy from said storage devices, a circuit, means responsive to discharging of energy from a first of said storage devices for applying an energy pulse to said circuit of a time diminishing amplitude determined by said storing means, means responsive to discharging of energy from the other of said storage devices for applying a second energy pulse to said circuit which is additive with respect to the first pulse applied thereto, means for closing said circuit when the additive energy pulses exceed a predetermined value greater than either of the pulses applied to said circuit, and electroresponsive means actuated upon closing of said circuit.

25. In a device of the class described, thecombination of a pair of condensers, means for gradually charging said condensers, means for selectively and substantially instantaneously discharging said condensers, a circuit, means responsive to discharging of a first of said condensers for applying a voltage pulse to said circuit of a time diminishing amplitude determined by said charging means, means responsive to discharging of the other of said condensers for applying a second voltage pulse to said circuit which is additive with respect to the first pulse applied thereto, means responsive to the additive potential applied to said circuit for closing said circuit upon the application of said second pulse thereto when less than a predetermined charge has been placed on said first condense-r, and electroresponsive means operated in response to closure of said circuit.

26. In a device of the class described, the combination of a pair of condensers, means for gradually charging said condensers, a pair of electronic tubes, means including said tubes for selectively and substantially instantaneously discharging said condensers, a circuit, means responsive to discharging energy from a first of said condensers for applying a potential pulse to said circuit of a time diminishing amplitude determined by said charging means, means responsive to discharging of the other of said condensers for applying a second potential pulse to said circuit which is additive with respect to the first pulse applied thereto, and electroresponsive means adapted to be actuated when the additive potential applied to said circuit exceeds a predetermined value which is greater than the maximum amplitude of either of the pulses applied to said circuit.

27. In a mine firing control circuit of the character disclosed, the combination of a control circuit including a normally nonconducting electron discharge device having a control electrode, a pair of normally nonconducting gaseous discharge devices, means for rendering said pair of devices conducting selectively, means controlled by operation of one of said devices for applying a voltage pulse of predetermined duration upon said control electrode, and means controlled by operation of the other of said devices for applying to said control electrode a voltage pulse which is additive with respect to said first pulse applied thereto thereby to render said electron discharge device conducting when the additive voltage exceeds a predetermined value. v

28. In a mine firing control system of the character disclosed, the combination of means including a transformer having a secondary winding for generating electric impulses of opposite polarity across said secondary winding in accordance with the magnetic signature of a vessel moving with respect to the mine, a pair of electron discharge devices each having a cathode, an anode defining a main gap with said cathode and a control electrode defining a control gap with said cathode, circuit means for connecting the main gaps of said devices in parallel, a normally charged condenser connected in parallel with said main gaps, circuit means including a portion of said secondary winding and connected across the main anode and control anode of one of said devices, and circuit means including the remaining portion of said secondary winding and connected across the main anode and control electrode of the other of said devices, said devices being rendered conducting selectively in accordance with the polarity of impulses appearing across said secondary winding, said condenser being discharged through either of said main gaps as the device individual thereto is rendered conducting, and said condenser providing a reference voltage for impulses generated by the secondary winding whereby the value of an impulse applied to the control electrode of one of the devices is effectively reduced when the other of the devices is rendered conducting.

29. In a mine firing control system of the character disclosed, the combination of a pair of normally non- 16. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, means responsive to production of a voltage of one phase for rendering said relaxation oscillator inoperative for a predetermined interval, means cooperating with said last named means and responsive to production of a voltage of opposite phase within a preterval has elasped for firing the mine, and means responsive to countermine shocks for operating said means for rendering said relaxation oscillator inoperative for a predetermined interval,

17. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, a source of electrical energy having positive and negative terminals, a pair of resistors, a pair of condensers each having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a potentiometer connected between said other plates of the condensers, a center tap on the potentiometer, means controlled by said voltages for selectively discharging said condensers in accordance with the phases of said voltages, means connected between said center tap and the negative terminal of said source for firing the mine when both of said condensers are discharged within a predetermined period of time, and means operatively connected to said potentiometer for rendering said relaxation oscillator inoperative for a predetersaid signals, a pair of electronic tubes each having an input circuit and an output circuit, means operatively connecting said input circuits to said magnetic amplifier network for selectively energizing said input circuits in accordance with the phases of said voltages, means operatively connected to said output circuits for firing the mine when both of said input circuits are energized within a predetermined period of time, and means connected to the output circuit of the first tube to be energized for momentarily rendering the other of said tubes inoperative.

19. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, a pair of electronic tubes each having an input circuit and an output circuit, means operatively connecting said input circuits to said magnetic amplifier network for selectively energizing said input circuits in accordance with the phases of said voltages, a condenser connected across said output circuits, means for charging said condenser, means operatively connected to said output circuits for firing the mine when both of said input circuits are energized within a predetermined period of time, and means in series with said condenser for mementarily rendering one of said tubes inoperative when the condenser is discharged by operation of the other of said tubes.

20. In a device of the character disclosed, the combination of an output circuit including a first gaseous discharge device having a control grid and adapted to be rendered conducting when the voltage on the control grid is increased by a predetermined amount above an initial bias potential thereon, second and third gaseous discharge devices, means for rendering the second discharge device conducting, means adapted to be ren dered effective as the second discharge device is rendered conducting to apply a first voltage to said control grid which exceeds a predetermined value for a predetermined interval of time, means for rendering the third discharge device conducting, and means adapted to be rendered effective as the third discharge device is rendered conducting to apply a second voltage to said control grid which is additive with respect to said first voltage applied thereto whereby the voltage on the grid is increased by said predetermined amount to render said first discharge device conducting when said second voltage is applied to the grid during said interval of time.

21. In a device of the character disclosed, the combination of an output circuit including a first gaseous discharge device having a control grid, means for rendering said first discharge device conducting to close said output circuit when the voltage on said control grid is increased by a predetermined amount above an initial bias potential thereon, means for applying said initial bias potential to the control grid, second and third gaseous discharge devices, means for rendering the second discharge device conducting, means for rendering the third discharge device conducting, means adapted to be rendered effective as the second discharge device is rendered conducting to apply a first voltage to said control grid which maintains the potential thereon in excess of a predetermined value for a predetermined interval of time, and means adapted to be rendered effective as the third discharge device is rendered conducting to apply a second voltage to said control grid which is additive with respect to said first voltage and adapted to increase the voltage on the grid by said predetermined amount to render said first discharge deconducting electron discharge devices each having a cathode, an anode defining a main gap with said cathode and a control electrode defining a control gap with said cathode, circuit means for connecting the main gap of said devices in parallel, a normally charged condenser connected in parallel with said main gaps and adapted to be discharged through either of the gaps as either of the devices individual thereto is rendered conductive, means including a transformer having a secondary winding for generating across the secondary winding a voltage impulse having successive positive and negative values in accordance with the magnetic signature of a vessel moving with respect to the mine, means for applying across the control gaps of said devices fixed bias potential of insufficient value to render said devices conducting, circuit means including one end of said secondary winding and connected across the anode and control electrode of one of said devices for elevating the bias potential thereon to a value rendering said device conducting in response to the positive value of the impulse appearing across said secondary winding, circuit means including the other end of said secondary winding and connected across the main anode and control electrode of the other of said devices for depressing the bias potential thereon in response to the positive value of said electrical impulse, the potential of said condenser serving as a reference voltage for said electrical impulse whereby the negative value thereof is suppressed upon discharge of the condenser as one of said devices is rendered conductive in response to the positive value of the impulse thereby to prevent operation of the other of said devices in response to the negative value of the impulse, circuit means controlled by said electron discharge devices for developing additively a voltage whose value is controlled by the time spaced relation of successive operations of the devices, and a mine firing circuit operatively connected to said last named circuit means and arranged to be operated by said additive voltage when the additive voltage reaches a predetermined value. 

1. In a device of the class described, the combination of a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate conNected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, electroresponsive means connected between said center tap and the negative terminal of said source of energy, and means for selectively discharging said condensers.
 2. In a device of the class described, the combination of a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, electroresponsive means connected between said center tap and the negative terminal of said source of energy, a pair of electronic tubes each having a plate circuit and a grid, means for connecting the plate circuits of said tubes across said condensers respectively, and means for selectively energizing each of said grids.
 3. In a device of the class described, the combination of a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, a pair of electronic tubes each having a plate circuit and a grid, means for connecting the plate circuits of said tubes across said condensers respectively, means for selectively energizing each of said grids whereby the electronic tubes will discharge the respective condensers, an electronic device having an input circuit and an output circuit, an electroresponsive device connected to said output circuit and controlled thereby, and means connecting said input circuit to said center tap and to the negative terminal of said source for firing said electronic device when both of said condensers are discharged within a predetermined period of time.
 4. In a device of the class described, the combination of means for producing signals of opposite polarities, a pair of energy storage devices, means for gradually storing energy therein, means controlled by said signals for selectively discharging energy from said energy storage devices in accordance with the polarities of said signals, a circuit, means for closing said circuit responsive to discharge by said discharging means of energy from one of said devices when less than a predetermined amount of energy has been stored in the other of said devices by said storing means, and electroresponsive means in said circuit operated upon closure thereof.
 5. In a device of the class described, in combination: a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, a pair of electronic tubes each having a plate circuit and a grid, means for connecting the plate circuits of saId tubes across said condensers respectively, means for selectively energizing each of said grids whereby the electronic tubes will discharge the respective condensers, an electronic device having an input circuit and an output circuit, an electroresponsive device connected to said output circuit and controlled thereby, means connecting said input circuit to said center tap and to the negative terminal of said source for firing said electronic device when both of said condensers are discharged within a predetermined period of time, a third condenser connected across said output circuit, and means to charge said third condenser within a predetermined interval.
 6. In a device of the character disclosed, the combination of a mine comprising means responsive to the magnetic field adjacent a moving paramagnetic object for producing signals of opposite polarities in accordance with changes in said magnetic field, a pair of energy storage devices, means for gradually storing energy therein, means controlled by said signals for selectively discharging the energy stored in said energy storage devices in accordance with the polarities of said signals, a circuit, means responsive to the amount of energy stored in said devices for controlling said circuit, and means in said circuit for firing the mine when the amount of energy stored in each of said devices is less than a predetermined maximum.
 7. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with changes in the magnetic field, a pair of condensers, means for gradually charging said condensers, means controlled by said signals for selectively discharging said condensers in accordance with the polarities of said signals, a circuit, means responsive to the charges on said condensers for controlling said circuits, and means in said circuit for firing the mine when the charge on each of said condensers is reduced to less than a predetermined value.
 8. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with changes in the magnetic field, a pair of condensers, means for gradually charging said condensers, a pair of electronic tubes, means controlled by said signals and including said tubes for selectively discharging said condensers in accordance with the polarities of said signals, a circuit, means responsive to the charges on said condensers for controlling said circuit, and means in said circuit for firing the mine when the charge on each of said condensers is reduced to less than a predetermined value.
 9. In a submarine mine for damaging the vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with changes in the magnetic field, a pair of condensers, means for slowly charging said condensers, a pair of electronic tubes, means controlled by said signals and including said tubes for selectively discharging said condensers in accordance with the polarities of said signals, a circuit, means responsive to the charges on said condensers for controlling said circuit, and means in said circuit for firing the mine when both of said condensers are discharged within a predetermined period of time.
 10. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a source of electrical energy having positive and negative terminals, a pair of resistors, a pair of condensers each having one plate connected to said positive terminals and the other plate connected in series with one of said resistors to said negative terminal, a potentIometer connected between said other plates of the condensers, a center tap on the potentiometer, a pair of electronic tubes each having a plate circuit and a grid, means for connecting the plate circuits of said tubes across said condensers respectively, means controlled by said signals for selectively energizing said grids in accordance with the polarities of said signals thereby to discharge the respective condensers, an electronic device having an input circuit and an output circuit, mine firing means connected to said output circuit and controlled thereby, and means connecting said input circuit to said center tap and to the negative terminal of said source for firing the electronic device when said condensers are both discharged within a predetermined period of time.
 11. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel for producing signals of opposite polarities in accordance with changes in the magnetic field, a source of electrical energy having positive and negative terminals, a pair of resistors, a first condenser having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a second condenser having one plate connected to said positive terminal and the other plate connected in series with the other of said resistors to said negative terminal, a potentiometer connected between said other plates of said condensers, a center tap on said potentiometer, means controlled by said signals for selectively discharging said condensers in accordance with the polarities of said signals, an electronic device having an input circuit and an output circuit, a mine firing device connected to said output circuit and controlled thereby, means connecting said input circuit to said center tap and to the negative terminal of said source for firing said electronic device when both of said condensers are discharged within a predetermined period of time, a third condenser connected to energize said output circuit, and means for charging said third condenser within a predetermined interval.
 12. In a system of the class described, the combination of means for producing signals of opposite polarities, means including a relaxation oscillator cooperating with said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, an electroresponsive device, means responsive to the production of voltages of opposite phase within a predetermined period of time for energizing said electroresponsive device, and means responsive to shocks applied to the system for rendering said relaxation oscillator inoperative for a predetermined interval.
 13. In a system of the class described, the combination of means for producing signals of opposite polarities, means including a relaxation oscillator cooperating with said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, means responsive to production of a voltage of one phase for rendering said relaxation oscillator inoperative for a predetermined interval, an electroresponsive device, and means cooperating with said last named means and responsive to the production of a voltage of opposite phase within a predetermined period of time after said predetermined interval has elapsed for energizing said electroresponsive device.
 14. In a system of the class described, the combination of means for producing signals of opposite polarities, means including a relaxation oscillator cooperating with said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, means responsive to production of a voltage of one phase for rendering said relaxation oscillator inoperative for a predetermined interval, an electroresponsive device, means cooperating with said last named means and responsive to the production of a voltage of opposite Phase within a predetermined period of time after said predetermined interval has elapsed for energizing said electroresponsive device, and means responsive to shocks applied to the system for operating said means for rendering said relaxation oscillator inoperative for a predetermined interval.
 15. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, means responsive to production of a voltage of one phase for rendering said relaxation oscillator inoperative for a predetermined interval, and means cooperating with said last named means and responsive to production of a voltage of opposite phase within a predetermined period of time after said predetermined interval has elapsed for firing the mine.
 16. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, means responsive to production of a voltage of one phase for rendering said relaxation oscillator inoperative for a predetermined interval, means cooperating with said last named means and responsive to production of a voltage of opposite phase within a predetermined period of time after said predetermined interval has elasped for firing the mine, and means responsive to countermine shocks for operating said means for rendering said relaxation oscillator inoperative for a predetermined interval.
 17. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, a source of electrical energy having positive and negative terminals, a pair of resistors, a pair of condensers each having one plate connected to said positive terminal and the other plate connected in series with one of said resistors to said negative terminal, a potentiometer connected between said other plates of the condensers, a center tap on the potentiometer, means controlled by said voltages for selectively discharging said condensers in accordance with the phases of said voltages, means connected between said center tap and the negative terminal of said source for firing the mine when both of said condensers are discharged within a predetermined period of time, and means operatively connected to said potentiometer for rendering said relaxation oscillator inoperative for a predetermined interval whenever one of said condensers is discharged.
 18. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, a pair of electronic tubes each having an input circuit and an output circuit, means operatively connecting said input circuits to said magnetic amplifier network for selectively energizing said input circuits in accordance with the phases of said voltages, means operatively connected to said output circuits for firing the mine when both of said input circuits are energized within a predetermined period of time, and means connected to the output circuit of the first tube to be energized for momentarily rendering the other of said tubes inoperative.
 19. In a submarine mine for damaging a vessel, the combination of a mine comprising means responsive to the magnetic field adjacent said vessel as the vessel moves through the water for producing signals of opposite polarities in accordance with changes in the magnetic field, a relaxation oscillator for generating intermittent pulses of current, a magnetic amplifier network energized by said relaxation oscillator and responsive to said signal producing means to produce voltages varying in phase in accordance with the polarities of said signals, a pair of electronic tubes each having an input circuit and an output circuit, means operatively connecting said input circuits to said magnetic amplifier network for selectively energizing said input circuits in accordance with the phases of said voltages, a condenser connected across said output circuits, means for charging said condenser, means operatively connected to said output circuits for firing the mine when both of said input circuits are energized within a predetermined period of time, and means in series with said condenser for mementarily rendering one of said tubes inoperative when the condenser is discharged by operation of the other of said tubes.
 20. In a device of the character disclosed, the combination of an output circuit including a first gaseous discharge device having a control grid and adapted to be rendered conducting when the voltage on the control grid is increased by a predetermined amount above an initial bias potential thereon, second and third gaseous discharge devices, means for rendering the second discharge device conducting, means adapted to be rendered effective as the second discharge device is rendered conducting to apply a first voltage to said control grid which exceeds a predetermined value for a predetermined interval of time, means for rendering the third discharge device conducting, and means adapted to be rendered effective as the third discharge device is rendered conducting to apply a second voltage to said control grid which is additive with respect to said first voltage applied thereto whereby the voltage on the grid is increased by said predetermined amount to render said first discharge device conducting when said second voltage is applied to the grid during said interval of time.
 21. In a device of the character disclosed, the combination of an output circuit including a first gaseous discharge device having a control grid, means for rendering said first discharge device conducting to close said output circuit when the voltage on said control grid is increased by a predetermined amount above an initial bias potential thereon, means for applying said initial bias potential to the control grid, second and third gaseous discharge devices, means for rendering the second discharge device conducting, means for rendering the third discharge device conducting, means adapted to be rendered effective as the second discharge device is rendered conducting to apply a first voltage to said control grid which maintains the potential thereon in excess of a predetermined value for a predetermined interval of time, and means adapted to be rendered effective as the third discharge device is rendered conducting to apply a second voltage to said control grid which is additive wiTh respect to said first voltage and adapted to increase the voltage on the grid by said predetermined amount to render said first discharge device conducting when said second and third devices are rendered conducting successively within said interval of time.
 22. In a device of the character disclosed, the combination of an output circuit including a first gaseous discharge device having a control grid, means for rendering said first discharge device conducting to close said circuit when the voltage on the control grid is increased by a predetermined amount above a predetermined value, a pair of gaseous discharge devices, means for rendering said pair of discharge devices conducting selectively, means adapted to be rendered effective as either one of said pair of discharge devices is rendered conducting to apply a first voltage to said control grid which maintains a potential thereon in excess of said predetermined value for a predetermined interval of time, and means adapted to be rendered effective as the other of said pair of discharge devices is rendered conducting during said interval of time to apply a second voltage to the control grid which is additive with respect to said first voltage thereon and increases the potential on the grid by said predetermined amount whereby the first discharge device is rendered conducting.
 23. In a device of the class described, the combination of a pair of energy storage devices, means for gradually storing energy therein, means for selectively and substantially instantaneously discharging energy from said storage devices, a circuit, means responsive to discharging of one of said storage devices for applying an energy pulse to said circuit, means responsive to discharging of the other of said storage devices within a predetermined time after discharging of the first of said devices for applying an energy pulse to said circuit which is additive with respect to said first-named pulse applied thereto, means for closing said circuit when the additive energy pulses applied thereto exceeds a predetermined value, and electroresponsive means in said circuit adapted to be operated as the circuit is closed.
 24. In a device of the class described, the combination of a pair of energy storage devices, means for gradually storing energy therein, means for selectively and substantially instantaneously discharging energy from said storage devices, a circuit, means responsive to discharging of energy from a first of said storage devices for applying an energy pulse to said circuit of a time diminishing amplitude determined by said storing means, means responsive to discharging of energy from the other of said storage devices for applying a second energy pulse to said circuit which is additive with respect to the first pulse applied thereto, means for closing said circuit when the additive energy pulses exceed a predetermined value greater than either of the pulses applied to said circuit, and electroresponsive means actuated upon closing of said circuit.
 25. In a device of the class described, the combination of a pair of condensers, means for gradually charging said condensers, means for selectively and substantially instantaneously discharging said condensers, a circuit, means responsive to discharging of a first of said condensers for applying a voltage pulse to said circuit of a time diminishing amplitude determined by said charging means, means responsive to discharging of the other of said condensers for applying a second voltage pulse to said circuit which is additive with respect to the first pulse applied thereto, means responsive to the additive potential applied to said circuit for closing said circuit upon the application of said second pulse thereto when less than a predetermined charge has been placed on said first condenser, and electroresponsive means operated in response to closure of said circuit.
 26. In a device of the class described, the combination of a pair of condensers, means for gradually charging said cOndensers, a pair of electronic tubes, means including said tubes for selectively and substantially instantaneously discharging said condensers, a circuit, means responsive to discharging energy from a first of said condensers for applying a potential pulse to said circuit of a time diminishing amplitude determined by said charging means, means responsive to discharging of the other of said condensers for applying a second potential pulse to said circuit which is additive with respect to the first pulse applied thereto, and electroresponsive means adapted to be actuated when the additive potential applied to said circuit exceeds a predetermined value which is greater than the maximum amplitude of either of the pulses applied to said circuit.
 27. In a mine firing control circuit of the character disclosed, the combination of a control circuit including a normally nonconducting electron discharge device having a control electrode, a pair of normally non-conducting gaseous discharge devices, means for rendering said pair of devices conducting selectively, means controlled by operation of one of said devices for applying a voltage pulse of predetermined duration upon said control electrode, and means controlled by operation of the other of said devices for applying to said control electrode a voltage pulse which is additive with respect to said first pulse applied thereto thereby to render said electron discharge device conducting when the additive voltage exceeds a predetermined value.
 28. In a mine firing control system of the character disclosed, the combination of means including a transformer having a secondary winding for generating electric impulses of opposite polarity across said secondary winding in accordance with the magnetic signature of a vessel moving with respect to the mine, a pair of electron discharge devices each having a cathode, an anode defining a main gap with said cathode and a control electrode defining a control gap with said cathode, circuit means for connecting the main gaps of said devices in parallel, a normally charged condenser connected in parallel with said main gaps, circuit means including a portion of said secondary winding and connected across the main anode and control anode of one of said devices, and circuit means including the remaining portion of said secondary winding and connected across the main anode and control electrode of the other of said devices, said devices being rendered conducting selectively in accordance with the polarity of impulses appearing across said secondary winding, said condenser being discharged through either of said main gaps as the device individual thereto is rendered conducting, and said condenser providing a reference voltage for impulses generated by the secondary winding whereby the value of an impulse applied to the control electrode of one of the devices is effectively reduced when the other of the devices is rendered conducting.
 29. In a mine firing control system of the character disclosed, the combination of a pair of normally non-conducting electron discharge devices each having a cathode, an anode defining a main gap with said cathode and a control electrode defining a control gap with said cathode, circuit means for connecting the main gap of said devices in parallel, a normally charged condenser connected in parallel with said main gaps and adapted to be discharged through either of the gaps as either of the devices individual thereto is rendered conductive, means including a transformer having a secondary winding for generating across the secondary winding a voltage impulse having successive positive and negative values in accordance with the magnetic signature of a vessel moving with respect to the mine, means for applying across the control gaps of said devices fixed bias potential of insufficient value to render said devices conducting, circuit means including one end of said secondary winding and connected across the anode and control electrode of one of said devices for elevating the biAs potential thereon to a value rendering said device conducting in response to the positive value of the impulse appearing across said secondary winding, circuit means including the other end of said secondary winding and connected across the main anode and control electrode of the other of said devices for depressing the bias potential thereon in response to the positive value of said electrical impulse, the potential of said condenser serving as a reference voltage for said electrical impulse whereby the negative value thereof is suppressed upon discharge of the condenser as one of said devices is rendered conductive in response to the positive value of the impulse thereby to prevent operation of the other of said devices in response to the negative value of the impulse, circuit means controlled by said electron discharge devices for developing additively a voltage whose value is controlled by the time spaced relation of successive operations of the devices, and a mine firing circuit operatively connected to said last named circuit means and arranged to be operated by said additive voltage when the additive voltage reaches a predetermined value. 